This application is a national stage of International Application No. PCT/EP/2007/008550, filed Oct. 2, 2007, which claims priority under 35 U.S.C. §119 to German Patent Application No. 10 2006 061 427.5, filed Dec. 23, 2006, the entire disclosure of which is herein expressly incorporated by reference.
The invention relates to a belt tensioning method and apparatus for restraining passengers of a vehicle.
German patent document DE 10139609 C1 discloses a method in which a possible or an actual accident is first sensed, such that a force can be applied to the vehicle passenger in good time (that is, at the latest, at the time of the first contact of the vehicle with an obstacle). This force acts with the impact direction, (the direction of the impact on the vehicle); thus a frontal impact, the direction is against the direction of travel. The force is applied to the passenger in such a manner that a constant (that is, even) force acts on the passenger over the entire brake path. When this is applied to a safety belt designed according to this method, removal of kinetic energy of the passenger is initiated early via by tightening belt slack, so that the passenger is delayed relative to the ground, even before a retaining effect is initiated through the safety belt system.
The known passive retaining action is initiated if the passenger is moved forward due to mass forces and is retained by the belt. A belt withdrawal block with force limitation normally acts then, which limits the load values on the chest. Energy can thus be removed over the entire brake path in an even manner, so that damaging acceleration peaks on the passenger are avoided. (The term “brake path” as used herein refers to the absolute path of the passenger in the vehicle, which is available for braking the passenger from the time of the first contact of the vehicle with the obstacle; it is thus composed of the dynamic total deformation of the vehicle and the possible pre-displacement path of the passenger within the passenger compartment.)
This method has the advantage that the restraint of the vehicle passenger starts early by a force applied thereto. The kinetic energy of the passenger can thus be reduced early, and the entire available path can be used. Unlike conventional retaining systems, no relative movement between the passenger and the vehicle needs be awaited, so that a retaining action is applied. The force can be applied to the vehicle passenger by several consecutively or simultaneously activated retaining systems. The force can also be applied corresponding to the impact direction by different retaining systems.
To increase passenger safety, a three point belt system is commonly provided for a normal vehicle seat with several belt tensioners, so that the belt slack in the belt system can be removed suddenly during an accident. The belt tensioners are designed so that the belt strap is applied to the body of the passenger in a tensioned manner, and without play, during an impact force, so that the passenger can take part in the vehicle deceleration as soon as possible. The retaining action is communicated by a belt withdrawal lock with force limitation. The known belt tensioners for removing the belt slack are not designed to exert a force on the passenger, which could effect an acceleration of the center of gravity.
The conventional pyrotechnic linear tensioners used in vehicles build up a force of 2-2.5 kN in a cylinder-piston unit within a time which is as short as possible (5-12 ms), which force is applied to retract the belt, and to remove its slack. The piston locks at the end of the tensioning path, so as to retain the passenger in the subsequent passive retaining phase, where he or she experiences a forward displacement, or to release the belt strap again against the resistance of a force limiting device, if present. With the locking of the piston, the pressure need not be maintained any more in the piston-cylinder unit. It is the trend that the tensioners reach the point of locking in a time that is as short as possible, so as to enter the locking then. The pressure in the piston-cylinder unit decreases quickly afterwards, so that the force limitation device can act in a defined manner in the belt withdrawal phase.
In German patent document DE 10139609 C1, the crash-conditional force peak is reduced in the belt strap by the delay of the center of gravity of the passenger brought forward relative to the ground, which is later used in the retaining phase. This method requires that high forces can be introduced via the safety belt system.
A safety belt system usually comprises a belt strap, which forms a lap belt between the belt end fitting and the belt lock. (The belt strap is deflected at the belt tongue, is guided to a deflector of a belt retractor arranged near the shoulder of a passenger, and forms the shoulder belt in the region between the belt lock and the deflector. The introduction of high forces by tensioning of the shoulder belt (e.g., by tensioning in the region of the belt retractor or at the belt lock) meets boundaries due to the limited pressure loading capacity of the chest region of the passenger. The high forces necessary for an acceleration of the passenger cannot be introduced at a sufficient height via the shoulder belt, especially as friction losses result by the deflection.
One object of the present invention is to improve the passenger protection afforded vehicle passenger restraint systems.
This and other objects and advantages are achieved by the method for retaining vehicle passengers and the belt tensioning system according to the invention, in which a possible accident is initially sensed, and a force acting in the direction of impact is exerted upon the passenger via a seat belt system, at the latest, whenever the first contact is made between the vehicle and the obstacle, or shortly thereafter (in particular, upon exceeding a threshold for vehicle deceleration). An improvement of 30% results already with a tensioning at the same time as with present-day vehicles, the ignition time for lock tensioners or the retractor tensioner; that is, shortly after the first contact with the obstacle, when the vehicle deceleration exceeds a threshold.
The activation of the safety belt system can also take place shortly before the impact in the sense of a pre-crash release, at the earliest, as soon as is known with certainty that the impact will take place. This is connected to a higher sensoric effort of a pre-crash sensor system.
The force is introduced by bilateral tensioning of a lap belt of a safety belt system, by tensioning from both sides with a force of typically 2000 N to 4500 N, and this force is maintained along a displacement path of the passenger over a period of at least 20 ms.
A bilateral tensioning of the lap belt is provided according to the invention, since the iliac wings of the passenger can receive much higher forces than the shoulder or chest of the passenger. The invention can be applied not only to three point safety belt systems, but also to safety belt systems which only have a lap belt or a separate lap belt.
The force exerted by early tensioning of the lap belt is decoupled from the delay pulse of the vehicle, which applies only with some delay in the full height due to the soft collapsible zones of present-day vehicles. A removal of kinetic energy of the passenger is initiated via the removal of belt slack, by delaying the passenger relative to the ground even before an inertia movement of the passenger caused by the impact can introduce a passive restraining action by the safety belt system. In other words: with a frontal impact, an acceleration pulse directed against the normal vehicle movement is impressed upon the passenger. The pulse or force entry is adjusted to the kinetic energy of the passenger, which is to be removed, with regard to duration and force level, wherein, as is known, the mass of the passenger and the vehicle speed are the significant magnitudes. The crash course (relative speed, crash gravity/the other party) to be expected enters the measurement as the available “brake path” for the passenger deceleration relative to the ground, as the use of the deformation path of the collapsible zone depends on the gravity of the accident.
The pulse initiation via the lap belt also offers an advantage in the kinematics of the upper body, as the pulse in the impact direction is forwarded to the upper body. The upper body is thereby accelerated in the impact direction, and immerses into the seat backrest and the seat cushion during this backward movement. The forward displacement of the upper body caused by the crash thus not only starts later, but a longer forward displacement path for the body, pelvis and head of the passenger is available.
It is an additional advantage that the passenger is drawn into the seat by the strength of the tensioning, whereby a longer forward displacement path is available for the passenger in the following passive retaining path. The need of a temporally longer tensioning requires that the tensioner provide a longer retraction path, which stands in good stead for a longer withdrawal path under the effect of a defined force limitation in the subsequent passive retaining phase, whereby a specific removal of kinetic energy of the passenger is possible.
It is a further advantage that all elasticities of the system (e.g., that of the belt strap or of the seat) are removed by the tensioning, so that a retaining path which is otherwise necessary for consuming elasticities, is omitted in the subsequent passive retaining phase and a longer retaining path is effectively available. A considerably earlier retention of the pelvis takes place via the seat cushion or other structural element of the seat, e.g., “anti-submarining” devices, seat wedges, etc.
A further embodiment of the method relates to a three point retaining system, where the belt strap is deflected at the belt tongue and is guided to a belt retractor arranged near the shoulder of a passenger, and where a third tensioner engages for introducing a force in the shoulder belt. According to the further embodiment, the belt strap section between the belt lock and the belt retractor (shoulder belt) is tensioned simultaneously with or before the lap belt, but the force introduced into the shoulder belt is limited to remove a belt slack. An optimum restraint of a passenger is possible with this combination of lap belt and shoulder belt tensioning, without the forces exerted by the tensioning systems exceeding the biomechanical loading capacity of the passenger. A reduction of the peak values is achieved compared to the present-day retaining systems.
In a further embodiment, specific control of the rearward displacement in the direction and acceleration can be achieved with the bilateral tensioning. The center of gravity of the passenger resulting in the direction of the seat backrest and/or seat cushion can for example be displaced by the bilateral tensioning with the same force of the lap belt during a frontal impact. One can for example react to a deviation of the impact region from the vehicle longitudinal direction e.g., during an oblique impact by a time delay in the tensioning of both sides.
Compared to the state of the art, the force in the lap belt is maintained at a high level of typically 2.0-4.5 kN over a sustained period between 20-100 ms before or at an early time after the start (t—0) of the crash. This requires a longer tensioning path, as the belt has to follow the retracting displacement and the reduction of the elasticities of the seat of the passenger.
The tensioners can have a pryotechnic release unit, which has the advantage that they can be released quickly, so that tensioning times are optimized, and passenger safety is increased considerably. But it is also possible to use other conventional release units, which have a pneumatic, hydraulic or electromotive drive. Mechanical drives using the stored energy of a compressed spring are also conceivable.
In an advantageous embodiment, the tensioners are formed with a cylinder-piston unit in a further development of linear tensioners of known construction. The first and second tensioner are linear drives with respectively one force transfer element, which is in operative connection with the belt lock or the end fitting. A longer tensioning path can be provided with an extension of the cylinder, a hollow cylinder, in which the piston is moved, to 100-150 mm, so that a total shortening of the lap belt by at least 200-300 mm can be achieved. So that the pressure in the cylinder-piston unit can be maintained over a longer period of 20-100 ms, sealing measures are usually necessary between piston, traction means and cylinder.
If the bilateral force introduction in the lap belt takes place by two independent tensioners (a first tensioner for the belt end fitting, and a second tensioner for the belt lock), the tensioning times, duration, and force levels of both tensioners can be adjusted independently, so that it can be reacted on the impact direction.
According to one embodiment, both tensioning systems are combined in a one-piece component, which can be integrated in the seat frame, for example, in a transverse traverse of the seat frame. This embodiment has the advantage that it can be completely preassembled, which has a positive effect on the assembly time.
The belt tensioning system—as one-piece or in several pieces—for tensioning the lap belt can be arranged under the seating area of the vehicle seat. Space is available there, so that integration of the tensioning system can be visually unobtrusive, and without loss of free space for the feet.
If both tensioners are arranged as transverse tensioners in a transverse manner under the seating area and are connected to the seat (e.g., by integration in a transverse traverse of the seat frame), it is possible to displace the seat together with the tensioning systems. In this manner, it is ensured that the tensioning systems always take up the same position relative to the belt end fitting and the belt lock, where the tensioning systems engage. Reliable functioning of the safety device is thus ensured. With an arrangement of the transverse tensioner between the seat adjustment rails of the seat, measures would have to be implemented to equalize a seat displacement in the length or the height.
In a preferred embodiment, both tensioners for the lap belt are integrated in a common seat-integrated component (in particular, the rear transverse traverse of the seat frame), and have a common release unit with a common working chamber, which is filled with gas under a high pressure when released by a common gas generator (e.g., a pyrotechnic ignition tablet).
In an advantageous further embodiment, the two working chambers of both tensioners are pneumatically connected to one another by an equalization, which volume ensures that the belt is retracted with the same force from both sides. The tensioners can be arranged in an axially offset manner in such a manner that both working chambers are aligned vertically. The two working chambers are then integrated into a common working chamber with the equalization volume, where the pressure build-up takes place. It is then also sensible to provide a common gas generator for the gas flow into the equalization volume. Only an ignition pill is thus necessary for a bilateral tensioning.
A connection element (especially a traction element) can be provided between the belt end fitting of the belt strap and the release unit, preferably in the form of a wire rope. Such a rope can transfer the traction forces reliably, which introduces the release unit into the connection element. Any other type of connection element which fulfills this object reliably is of course also possible.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.